Control for air spring pressures in free-piston units



Aug. 26, 1941. "K. c. cooPzl a 2,426,297-

CONTROL FOR AIR SPRING FRESSURES 1N FREE-PISTON UNITS Filed Aug. 23,1944 SSheati-Sheet 1 1/3 O 0' 0 al 0 O O 0 O O O (D O 0 'T H 2 .f K Q mZ o o B Q 090 3,

o o 0 0 v 2 0 0 0 (0 0O 30 O 0000 .INV-ENTOR Aug. 26, 1947. K. c. COOPER97 COK'I'ROL FOR AIR SPRING PRESSURES IIIfREB-PISTON UNITS Filed Aug.23, 1944 3.5haots-Shoot 2 a x g INVENTOR are always maintained PatentedAug. 26, 1947 CONTROL FOB AIR SPRINGPRESSUBES IN FREE-PISTON UNITSKenneth 0. Cooper, Portland, oc'nnl, assign to United AircraltCorporation, East Hartford, Conn., a corporation of Delaware ApplicationAugust 2:, 1944, Serial No. 550,816

2 Claims. (Cl- 230-46) which includes racks 34 and 38, Fig. 2, extendingfrom pistons l6 and I8 and engaging a pinion 38 on a shaft 40.

Intake manifold 42, which extends around the engine and compressorcylinders, conducts air to intake valves M in the heads of thecompressor cylinders through which air alternately enters of thisinvention is the automatic control of the pressure in the air springs.

The copending application of tinsky, Serial No. 550,883, filed. August23, 1944, issued, on May 13, 1947, as Patent No. 2,420,t83 discloses astroke indicator adapted for adjusting one-or more of the operatingcharacteristics of the unit tomaintain the desired piston stroke. Theinvention is directed to the structure by which the air spring pressuremay be controlled in response to changes in piston stroke.

A feature of the invention is a compression control for the gas in theair spring which will ad just the pressure in the air springs asafunction of the engine exhaust pressure to compensate for varying loadson the compressor. Another feature is a compression control which isactuated in response both to changes in piston stroke and to changes inexhaust pressure.

Other objects and advantages will be apparent from the specification andclaims, and from the accompanying drawings which illustrate anembodiment of the invention.

Fig. 1 is a sectional view through the unit.

his". 2 is a fragmentary sectional view oi the restraining linkage.

Fig. 3 is a diagrammatic sion control and the stroke control. 1

The unit shown includes an engine cylinder to having reciprocatingpistons l2 and it to which compressor pistons lb and it in cylinders illand 22 are integrally connected. Sleeves 2t and 2E attached to thecompressor pistons complete the reciprocating piston assemblies. Thesleeves in combination with stationary pistons 23 and to over which theyreciprocate form air spring cylinders.

The piston assemblies are-moved'apar by the burning of fuel injectedinto engine cylinder at through one or more nozzles 32. Air compressedin the air spring'cylinders on the power stroke returns the pistonassemblies. The assemblies at equal distances from the center of theengine cylinder view of the compresby a linkage,

opposite end or the compressor clyllnders. The

' compressed air leaves the cylinders through discharge valves 46, alsoat opposite ends of the compressor cylinders and asses into a centralscavenge chamber 48 and end chambers 50 and 52. These chambers may beinterconnected by a scavenge manifold, not shown.

Compressed gas from the scavenge chambers enters engine ports 56 and 56which are uncovered by pistons l2 and H at theend of the power stroke,thereby permitting air to be blown through the engine cylinder. Gas inthe engine cylinder is discharged through exhaust port 58 into exhaustmanifold it.

The-position oi! the piston at the inner'end of its stroke is indicatedby a master control it actuated by a cam 64 mounted on the shaft it asshown iii-Fig. 3. Since the pinion 38 is oscillated directly from thepistons, the movement of 'nected by a passage cam 84 is directlyproportional to the piston stroke. 4

Fluid under pressure from a constant pressure source enters a passage 66in a casing 6t through a conduit III. This passage intersects a bore l2adjacent the outer end and a throttling screw it controls the rate offlow into bore 12. A branch passage 16 from passage 66 connects with aport 18 in bore 12. A plunger 80' in bore ll has a groove 82 whichconnects a port 84 alternately with port 18 or with a port 86. Port fitis con- Bil to the inner end of bore I2. Port 88 is connected by achannel lit in casspaced grooves ing it and in an adjacentcasing 92 tothe inner (left hand) end of a bore 94 in casing 92.

A piston 96 in bore 94 is moved to the right by a calibrated spring 98.A plunger I00 extends through the piston and carries at its outer end apush rod IM. This rod has a roller Hi5 which is held against cam 64 by aspring I06. Plunger Hill has a central passage I08 connecting with litand means of parts H3 and H5 respectively. Groove H2 aligns withopenings 4 in a sleeve H6 groove llll is adapted to be uncovered by theend of sleeve H6 as'the plunger is moved to the right by the earn as thepistons approach the inner ends of their stroke. Fluid under pressurefrom the right hand end H2 in the plunger by' of bore 12 enters theouter end of bore 94 through a connecting channel I I8 moving piston 96against the action of spring 98. As plunger I is moved to the right bycam 64 groove 0 is uncovered by sleeve I I6 to permit discharge of fluidfrom the outer end of bore 94. The pressure in the outer end of bore 94thus varies in accordance with the compression of spring 98 and as thepiston stroke becomes shorter the piston 96 moves inward (to the left)increasing the spring tension and increasing the pressure at theright-hand end of bore 94 such that the change in pressure isproportional to in the end position of the stroke.

Since the right-hand end of bore 12 is connected directly to the end ofbore 94, the change in pressure on the outer (right hand) end of theplunger 80 is also proportional to the change in the position of thepiston stroke. The pressure on the opposite end of the plunger 80, whichbalances the pressure on the outer end, must vary in the same manner andis accomplished by the above-described porting in bore I2. In this waythe pressure in the discharge conduit I20 is proportional to the spacingof the actual end of the piston stroke from the extreme inner positionof the piston and changes in pressure in this conduit will beproportional to changes in the end position of the piston stroke. Thispressure (and change in pressure) may indicate on a gauge I22 the exactposition of the end of the piston stroke and maybe used for actuatingthe compression control device for the air springs.

The outer end of plunger I 00 may reciprocate in a chamber I24 which maybe connected by a conduit I28 to the conduit I30 from the inner end ofbore 94. Conduit I28 may be connected to a sump, not shown. Throttlingscrew I4 in passage 66 permits adjustment of the sensitivity of thecontrol. A bellows I32 connected to passage H8 reduces pressure surgesin the device.

The compression control includes a casing I38 having a bore I40 in whicha plunger I42 is mounted. A port I44 is connected by a conduit I46 to asource of gas under pressure and an outlet port I48 is connected by aconduit I50 to the the change air spring. Plunger I42 is moved to theright by a spring I52, the tension of which is adjusted by a nut I54. Apiston I56 in a bore I58 in a cap I59 on casing I 38 engages aprojecting pin I60 on the plunger. Fluid under pressure from the innermaster control enters the end of bore I58 from conduit I20 to moveplunger I42 against the action of spring I52. Piston I56 may have asmall vent I62 and the inner end of bore I58 may be vented by a conduitI64 connecting with a sump.

If the fluid pressure from the master control increases, indicating thatthe inner end position of the piston stroke is moving away from innerdead center, plunger I 42 is moved to the left so that a groove I66 inplunger I42 connects inlet port I44 and outlet port I48 to admit gas tothe air springs for increasing the pressure in the air springs and thusmoving the stroke inward again. If the fluid pressure fromthe mastercontrol decreases, spring I52 moves plunger I42 beyond the positionshown to close port I44 and connect port I48 to a vent I61 for reducingthe air spring pressure.

In operation fluid under pressure enters the master control past thethrottle valve 14, through the right-hand end of bore 12 and into therighthand end of bore 94 building up pressure in bore 94 until thepiston 96 is moved far enough to the left to uncover groove IIO. At thistime the pressure at the right of piston 96 will correspond to thespring force acting on the piston and will be indicated on the indicator22 since the pressure at the right-hand end of bore '52 is maintainedthe same as the pressure at the left-hand end by reason of the controlefiected by plunger 88 as it moves relative to the inlet port i6. Sincethe plunger I00 is reciprocated in unison with the piston assembly ofthe free-piston unit through the medium of cam 64, its position withinbore 94 is indicative of the position of the engine piston within theengine cylinder. The extreme hand position of plunger the extreme innerend piston.

With the free-piston unit stopped, the pressure indicated on gauge I22will be the pressure required to compress the spring 90 enough to per-I00 would correspond to position of the engine -mit piston 96 to uncoverthe groove H8. Thus,

as the spacing of the piston assembly of the unit from its extreme endposition increases, the pressure indication-will also increase and thepressure in duct I20 will similarly increase.

When the free-piston unit is operating, the plunger- I00 is reciprocatedwithin the piston 96 in unison withthe reciprocation of the pistonassembly of the free-piston unit and the piston 96 is moved to the leftby the pressure fluid acting upon it until the plunger I00 barelyuncovers the groove IIO on each stroke. Thus, the piston 96 seeks aposition, the spacing of which, from its extreme right-hand endposition,is proportional to the spacing of the actual inner-end of the pistonstroke from its extreme inner end position.

As the stroke of the piston assembly shortens, thereby causing theactual inner end of the piston stroke to move away from the extremeinner end position, the pressure increases in duct I28 as determined bythe \spring 90 and operates on piston I56 to move the valve I42 to theleft against the eflect of spring I52 to admit compressed gas from theport I 44 into the duct I50 and thence to the air spring, therebyincreasing the gas pressure within the air spring for increasing thelength of the piston stroke to restore the unit to its normal operation.If the stroke of the piston assembly of the free-piston unit lengthensor if the inner ends of the piston strokes begin to move more and moretoward extreme inner end position, the pressure drops in the duct I20and permits the valve I42 to move to the right under the influence ofspring I52 to vent the air spring through the port I6 In addition tocontrolling the air spring pressure from the inner master control, thispressure may also be dependent upon the engine exhaust pressure. Toaccomplish this, the exhaust duct 60 is connected by a conduit I68 tothe end of casing I38 opposite to the piston I 56. In this way when theexhaust pressure is low, the pressure from the inner master control actsonly against spring I52. As the exhaust pressure increases, however,this pressure assists spring I52 and a greater pressure from the innermaster control is necessary to move plunger I42 to establish gasconnection between ports I44 and I48.

If the exhaust pressure of the unit increases, the compression pressureat the inner end of the stroke will also increase if the piston strokeremained the same. It may be desirable to maintain a constantcompression pressure at the inner end of the piston stroke and to dothis, the inner end of the piston stroke must move away from thecenter-of the engine as the exhaust pressure right- It is to beunderstood that the invention is not limited to the specific embodimentherein illustrated, and described, but may be used in other ways withoutdeparture from its spirit as defined by the following claims.

I claim:

1. A free -piston unit having an engine cylinder, opposed pistons in thecylinder and air springs for moving the pistons on the compressionstroke, in combination with a control device, means for procuringchanges in the control device in response to changes in the inner endpositions of the piston strokes, and means actuated by said controldevice for adjusting the air spring pressures, said last means includingmeans for supplying gas to the air springs and means for con trollingthe rate at which gas is supplied to the air spring.

2. A free-piston unit having an engine cylinder, opposed pistons in thecylinder and air springs for moving the pistons on the'compressionstroke, in combination with a control device, means for procuringchangesin the control device in response. to changes in the inner end positionsof the piston strokes, means actuated by said control device foradjusting the air spring REFERENCES crrnn The following references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,090,709 Steiner Aug. 24, 19372,178,310 Fescara Oct. 31, 1939 2,215,326 J anicke Sept. 17, 19402,162,967 Pescara June 20, 1939 2,168,829 Pescara Aug. 8, 1939 2,016,613Pescara Oct. 8, 1935 2,064,976 Janicke Dec. '22, 1936 2,108,890 JanickeFeb. 22, 1938 2,147,935 Steiner Feb. 21, 1939 2,178,310 Pescara Oct. 31,1939 2,173,311 Pescara Oct. 31, 1939 2,189,497 Pescara Feb. 6, 19402,408,089 Muntz Sept. 24, 1946 V FOREIGN PATENTS Number Country Date541,779 Great Britain Dec. 11, 1941

